Millions of Indian citizens across 96 constituencies began casting their ballots on Monday as the country's gigantic, six-week-long election edges past its halfway mark.

Indian Prime Minister Narendra Modi is seeking a third straight term with an eye on winning a supermajority in Parliament.

Monday’s polling in the fourth round of multi-phase national elections across nine states and one union territory will be pivotal for Modi’s Hindu nationalist Bharatiya Janata Party (BJP), as it includes some of its strongholds in states like Uttar Pradesh and Madhya Pradesh.

Crucial seats in Maharashtra and Bihar states, where the BJP governs in alliances with regional parties, were also up for grabs in this phase.

In Bihar’s Samastipur city, hundreds of voters lined up at a polling station that opened at 7am amid tight security arrangements. Voters said they were concerned about rising food prices, lack of employment and economic development in the state.

Most polls predict a win for Modi and his BJP, which is up against a broad opposition alliance led by the Indian National Congress and powerful regional parties.

The staggered election will run until June 1 and nearly 970 million voters, more than 10 percent of the world’s population, will elect 543 members to the lower house of Parliament for five years.

The votes are scheduled to be counted on June 4. (AP)